Acral myxoinflammatory fibroblastic sarcoma (AMSF), also termed myxoinflammatory fibroblastic sarcoma (MSF), is a rare, low-grade, soft tissue tumor that the World Health Organization (2020) classified as in the category of rarely metastasizing fibroblastic and myofibroblastic tumors. [1] It is a locally aggressive neoplasm that often recurs at the site of its surgical removal. However, it usually grows slowly and in only 1–2% of cases spreads to distant tissues. [2]
AMSF tumors commonly develop in the subcutaneous tissues of the arms or legs of adults with an equal incidence (~1 per million individuals [2] ) in males and females. [3] These tumors are composed of a prominent inflammatory cell infiltrate admixed with cells that have highly variable microscopic appearances, [4] including, in particular, distinctively large, neoplastic epithelioid cells, i.e. cells resembling epithelial cells, [5] and lipoblast-like fibroblastic cells containing multiple vacuoles. [6] The variable microscopic appearances of AMSF tumors have made them difficult to correctly diagnose in many cases. [4]
AMSF lesions are treated by surgical resection with the goal to remove all tumor tissue in order to reduce local recurrences. Repeated local recurrences are treated by repeated surgical resections. In extreme cases, a combination of radiation therapy with surgical resection or amputation of an involved appendage has been used to treat these tumors. Chemotherapy of localized, recurrent, and/or metastatic disease has not yet been shown to be a useful treatment strategy for AMSF. [2]
AMSF tumors typically occur in adults (average age: 40 years), [4] but have been reported in individuals aged 4 to 91 years. [7] Individuals commonly present with a subcutaneous [5] or less commonly intramuscular [2] tumor located in an acral (i.e. distal), dorsal (i.e. posterior side) of a limb: about two-thirds of cases occur in a finger, hand, wrist, foot, or ankle. [4] In a minority of cases, these tumors have developed in the upper arm, thigh, shoulder, inguinal area (i.e. groin or lower, lateral abdomen), [5] upper back, neck, temple area of the head, and in one case, the nose. [7] Individuals commonly present with a painless, slowly growing mass in one of these areas. [7] The size of these tumors has ranged from 1.5 to 18 cm, [8] although one AMSF tumor that spanned the supraclavicular and infraclavicular fossa areas had a maximum diameter of 25 cm [9] and another AMSF tumor in the thigh had a maximum diameter of 30 cm. [10] Individuals often re-present with a recurrence of their tumor at the site of its previous surgical removal or, in rare cases, present with metastatic disease. [11]
As examined by gross pathology, AMSF tumors are typically lobulated, with gelatinous, fleshy, or firm areas that vary in color and texture; they are most often localized to subcutaneous adipose tissue but may infiltrate into nearby tissues. [4] Histopathologic microscopic examinations of hematoxylin and eosin stained tumors characteristically show spindle-shaped cells admixed with prominent inflammation-like areas containing a mixture of neutrophils, lymphocytes, and plasma cells. The areas of these lesions that contain spindle cells are often also occupied by distinctively large, variably-shaped epithelioid cells that have vesicle-laden nuclei and acidophilic (readily stained with acid dyes) nucleoli. These cells have been termed Reed-Sternberg cell-like, virocyte-like (i.e. cells which, similar to some viruses, have sticklike protrusions), and ganglion cell-like. The tumors may also contain large vacuolated pseudolipoblasts (i.e. cells that resemble lipoblasts). These various cell types are embedded in a myxoid (i.e. more blue or purple compared to normal connective tissue because of excessive uptake of the hematoxylin stain) and collagen fiber-laden tissue background. [5] In addition to the cited cell types, the tumors may contain degenerated, dying, and or dead cells and large histiocyte-like cells that have engulfed other cells, usually neutrophils (this cell-engulfing phenomenon is termed emperipolesis). [4] In one large study, emperipolesis of white blood cells appeared to be a helpful indicator of AMSF. [10] ) The proportions, numbers, and types of these cells varies greatly among cases and thereby may present diagnostic challenges. For example, AMSF tumors can have dense inflammatory infiltrates which obscure other cell types and thereby suggest that the lesion is a purely inflammatory reaction. [5]
A recent immunohistochemical immunostaining small study on AMSF tumor tissue detected cells that expressed the vimentin protein in almost all cases; expressed MUC1 (also termed EMA), CD31, CD34, CD68, and PDPN proteins in a variable number of cases; and did not express CD45, CD15, CD30, HMB-45, MLANA (also termed Melan-A), desmin, GFAP, or S100 proteins. [5] Earlier studies had reported that these cells express vimentin, periodic acid-Schiff, CD34, CD68, and S100 proteins in many cases but not MUC1, cytokeratin, or desmin proteins. [9] [12] The expression profiles of these proteins, which sometimes differed in different studies, have not been helpful in identifying a tumor as an AMSF. [2] [5]
Several abnormalities in the chromosomes and genes have been variably reported in the neoplastic cells of a minority of AMSF cases. These abnormalities include: 1) loses in chromosome 3 or chromosome 13; [7] 2) a translocation between the TGFBR3 gene located in band 22.1 on the short (or "p") arm of chromosome 1 and the MGEA5 gene located in band 24 of the long (or "q") arm of chromosome 10; 3) the presence of a ring chromosome that is associated with the overexpression of the VGLL3 protein (VGLL3 is also overexpressed in various high-grade sarcomas) as well as the overexpression of the CHMP2B protein; [4] and 4) incompletely defined fusions of the BRAF gene located in band 34 on the q arm of chromosome 7 [13] with other genes. [2] These molecular findings have not as yet been shown to be involved in the development of, or helpful in diagnosing, AMSF. [5]
Since the immunostaining, abnormal gene, and abnormal chromosome profiles of AMSF tissues are non-specific, the diagnosis of these tumors rests mostly on patient presentation and tumor histopathologic grounds. AMSF may be confused with other myxoid-rich soft tissue tumors such as myxoid liposarcoma (MyxLPS), myxofibrosarcoma (MyxoFS), and extra-skeletal myxoid chondrosarcoma (EMC). MyxoFS tumors more often occur in a proximal rather than acral location, consist of more prominent capillary vessels, and lack inflammatory and VRS-like cells. MyxLpS tumors consist of a monotonous cell population arranged in discrete myxoid-cellular clusters with conspicuous thin branching capillaries in a "chicken-wire pattern". [5] EMC rumors: contain an epithelioid/rounded cell population arranged in single cells, clusters, or linear cords; lack VRS-like cells; and have neoplastic cells that express diagnostic fusion genes involving the NR4A3 gene fused with either the EWSR1 or TAF15 gene. Some nodular fasciitis and proliferative fasciitis lesions may have myxoid areas but unlike AMSF tumors are rapidly growing, contain ganglion-like cells with only rare inflammatory cells, [5] and may regress without treatment. [14] [15] Other lesions that frequently present in acral areas of the extremities such as hemosiderotic fibrolipomatous tumor, [16] epithelioid sarcoma, synovial sarcoma, acral fibromyxoma, giant cell tumor of tendon sheath, and clear cell sarcoma are usually distinguished from AMSF based on their clinical presentations, gross pathologies, histopathologies, and/or neoplastic cell expressions of marker proteins, abnormal chromosomes, and/or abnormal genes. [5]
Whenever possible, the first-choice treatment of AMSF tumors is surgical resection with wide margins in order to remove all neoplastic tissue. This treatment can be curative particularly when all tumor is removed but recurrences have developed at the sites of their surgical removals in 22% to 67% of all cases. [2] Repeated recurrences at a site are commonly treated with repeated surgical resections with some patients treated with several resections at a site. [11] Amputations of an extremity may be considered when wide resection fails to preserve a functional lower extremity or when multiple resections are consistently followed by recurrences. [2] Preoperative or postoperative radiation therapy may have a role in treating these tumors, especially in cases were surgical removal leaves tumor tissue behind. In a minority of cases (i.e. 1–2%), AMSF tumors metastasize to distant tissues. [2] Radiation and chemotherapy either alone or in combination have been used to treat metastatic disease. [11] [12] [17] While radiation therapy has been associated with improved local control, [4] its overall efficacy has not been fully studied and remains unclear. [4] [18] The role of chemotherapy in the treatment of local and metastatic disease is also unclear. [2]
This lesion was first described in 1998 independently in three publications which named the disorder "acral myxoinflammatory fibroblastic sarcoma", [19] "inflammatory myxoid tumor of the soft parts with bizarre giant cells", [20] and "inflammatory myxohyaline tumor of distal extremities with virocyte or Reed-Sternberg-like cells". [21]
Dermatofibrosarcoma protuberans (DFSP) is a rare locally aggressive malignant cutaneous soft-tissue sarcoma. DFSP develops in the connective tissue cells in the middle layer of the skin (dermis). Estimates of the overall occurrence of DFSP in the United States are 0.8 to 4.5 cases per million persons per year. In the United States, DFSP accounts for between 1 and 6 percent of all soft tissue sarcomas and 18 percent of all cutaneous soft tissue sarcomas. In the Surveillance, Epidemiology and End Results (SEER) tumor registry from 1992 through 2004, DFSP was second only to Kaposi sarcoma.
Liposarcomas are the most common subtype of soft tissue sarcomas, accounting for at least 20% of all sarcomas in adults. Soft tissue sarcomas are rare neoplasms with over 150 different histological subtypes or forms. Liposarcomas arise from the precursor lipoblasts of the adipocytes in adipose tissues. Adipose tissues are distributed throughout the body, including such sites as the deep and more superficial layers of subcutaneous tissues as well as in less surgically accessible sites like the retroperitoneum and visceral fat inside the abdominal cavity.
Nodular fasciitis (NF) is a benign, soft tissue tumor composed of myofibroblasts that typically occurs in subcutaneous tissue, fascia, and/or muscles. The literature sometimes titles rare NF variants according to their tissue locations. The most frequently used and important of these are: cranial fasciitis and intravascular fasciitis. In 2020, the World Health Organization classified nodular fasciitis as in the category of benign fibroblastic/myofibroblastic tumors. NF is the most common of the benign fibroblastic proliferative tumors of soft tissue and exceeds in frequency any other tumor or tumor-like lesion in this group of tumors.
Giant cell fibroblastoma (GCF) is a rare type of soft-tissue tumor marked by painless nodules in the dermis and subcutaneous tissue. These tumors may come back after surgery, but they do not spread to other parts of the body. They occur mostly in boys. GCF tumor tissues consist of bland spindle-shaped or stellate-shaped cells interspersed among multinucleated giant cells.
Fibrous hamartoma of infancy (FHI) is a rare, typically painless, benign tumor that develops in the subcutaneous tissues of the axilla, arms, external genitalia, or, less commonly, various other areas. It is diagnosed in children who are usually less than 2 years old or, in up to 20% of cases, develops in utero and is diagnosed in an infant at birth.
Clear cell sarcoma is a rare form of cancer called a sarcoma. It is known to occur mainly in the soft tissues and dermis. Rare forms were thought to occur in the gastrointestinal tract before they were discovered to be different and redesignated as GNET.
Extraskeletal myxoid chondrosarcoma (EMC) is a rare low-grade malignant mesenchymal neoplasm of the soft tissues, that differs from other sarcomas by unique histology and characteristic chromosomal translocations. There is an uncertain differentiation and neuroendocrine differentiation is even possible.
Low-grade fibromyxoid sarcoma (LGFMS) is a rare type of low-grade sarcoma first described by H. L. Evans in 1987. LGFMS are soft tissue tumors of the mesenchyme-derived connective tissues; on microscopic examination, they are found to be composed of spindle-shaped cells that resemble fibroblasts. These fibroblastic, spindle-shaped cells are neoplastic cells that in most cases of LGFMS express fusion genes, i.e. genes composed of parts of two different genes that form as a result of mutations. The World Health Organization (2020) classified LGFMS as a specific type of tumor in the category of malignant fibroblastic and myofibroblastic tumors.
Inflammatory myofibroblastic tumor (IMT) is a rare neoplasm of the mesodermal cells that form the connective tissues which support virtually all of the organs and tissues of the body. IMT was formerly termed inflammatory pseudotumor. Currently, however, inflammatory pseudotumor designates a large and heterogeneous group of soft tissue tumors that includes inflammatory myofibroblastic tumor, plasma cell granuloma, xanthomatous pseudotumor, solitary mast cell granuloma, inflammatory fibrosarcoma, pseudosarcomatous myofibroblastic proliferation, myofibroblastoma, inflammatory myofibrohistiocytic proliferation, and other tumors that develop from connective tissue cells. Inflammatory pseudotumour is a generic term applied to various neoplastic and non-neoplastic tissue lesions which share a common microscopic appearance consisting of spindle cells and a prominent presence of the white blood cells that populate chronic or, less commonly, acute inflamed tissues.
Mammary-type myofibroblastoma (MFB), also named mammary and extramammary myofibroblastoma, was first termed myofibrolastoma of the breast, or, more simply, either mammary myofibroblastoma (MMFB) or just myofibroblastoma. The change in this terminology occurred because the initial 1987 study and many subsequent studies found this tumor only in breast tissue. However, a 2001 study followed by numerous reports found tumors with the microscopic histopathology and other key features of mammary MFB in a wide range of organs and tissues. Further complicating the issue, early studies on MFB classified it as one of various types of spindle cell tumors that, except for MFB, were ill-defined. These other tumors, which have often been named interchangeably in different reports, are: myelofibroblastoma, benign spindle cell tumor, fibroma, spindle cell lipoma, myogenic stromal tumor, and solitary stromal tumor. Finally, studies suggest that spindle cell lipoma and cellular angiofibroma are variants of MFB. Here, the latter two tumors are tentatively classified as MFB variants but otherwise MFB is described as it is more strictly defined in most recent publications. The World Health Organization in 2020 classified mammary type myofibroblastoma tumors and myofibroblastoma tumors as separate tumor forms within the category of fibroblastic and myofibroblastic tumors.
Proliferative fasciitis and proliferative myositis (PF/PM) are rare benign soft tissue lesions that increase in size over several weeks and often regress over the ensuing 1–3 months. The lesions in PF/PM are typically obvious tumors or swellings. Historically, many studies had grouped the two descriptive forms of PF/PM as similar disorders with the exception that proliferative fasciitis occurs in subcutaneous tissues while proliferative myositis occurs in muscle tissues. In 2020, the World Health Organization agreed with this view and defined these lesions as virtually identical disorders termed proliferative fasciitis/proliferative myositis or proliferative fasciitis and proliferative myositis. The Organization also classified them as one of the various forms of the fibroblastic and myofibroblastic tumors.
Fibroblastic and myofibroblastic tumors (FMTs) develop from the mesenchymal stem cells which differentiate into fibroblasts and/or the myocytes/myoblasts that differentiate into muscle cells. FMTs are a heterogeneous group of soft tissue neoplasms. The World Health Organization (2020) defined tumors as being FMTs based on their morphology and, more importantly, newly discovered abnormalities in the expression levels of key gene products made by these tumors' neoplastic cells. Histopathologically, FMTs consist of neoplastic connective tissue cells which have differented into cells that have microscopic appearances resembling fibroblasts and/or myofibroblasts. The fibroblastic cells are characterized as spindle-shaped cells with inconspicuous nucleoli that express vimentin, an intracellular protein typically found in mesenchymal cells, and CD34, a cell surface membrane glycoprotein. Myofibroblastic cells are plumper with more abundant cytoplasm and more prominent nucleoli; they express smooth muscle marker proteins such as smooth muscle actins, desmin, and caldesmon. The World Health Organization further classified FMTs into four tumor forms based on their varying levels of aggressiveness: benign, intermediate, intermediate, and malignant.
Lipofibromatosis-like neural tumor (LPF-NT) is an extremely rare soft tissue tumor first described by Agaram et al in 2016. As of mid-2021, at least 39 cases of LPF-NT have been reported in the literature. LPF-NT tumors have several features that resemble lipofibromatosis (LPF) tumors, malignant peripheral nerve sheath tumors, spindle cell sarcomas, low-grade neural tumors, peripheral nerve sheath tumors, and other less clearly defined tumors; Prior to the Agaram at al report, LPF-NTs were likely diagnosed as variants or atypical forms of these tumors. The analyses of Agaram at al and subsequent studies uncovered critical differences between LPF-NT and the other tumor forms which suggest that it is a distinct tumor entity differing not only from lipofibromatosis but also the other tumor forms.
Myxofibrosarcoma (MFS), although a rare type of tumor, is one of the most common soft tissue sarcomas, i.e. cancerous tumors, that develop in the soft tissues of elderly individuals. Initially considered to be a type of histiocytoma termed fibrous histiocytoma or myxoid variant of malignant fibrous histiocytoma, Angervall et al. termed this tumor myxofibrosarcoma in 1977. In 2020, the World Health Organization reclassified MFS as a separate and distinct tumor in the category of malignant fibroblastic and myofibroblastic tumors.
Sclerosing epithelioid fibrosarcoma (SEF) is a very rare malignant tumor of soft tissues that on microscopic examination consists of small round or ovoid neoplastic epithelioid fibroblast-like cells, i.e. cells that have features resembling both epithelioid cells and fibroblasts. In 2020, the World Health Organization classified SEF as a distinct tumor type in the category of malignant fibroblastic and myofibroblastic tumors. However, current studies have reported that low-grade fibromyxoid sarcoma (LGFMS) has many clinically and pathologically important features characteristic of SEF; these studies suggest that LGSFMS may be an early form of, and over time progress to become, a SEF. Since the World Health Organization has classified LGFMS as one of the malignant fibroblastic and myofibroblastic tumors that is distinctly different than SEF, SEF and LGFMS are here regarded as different tumor forms.
The FET protein family the EWSR1 protein encoded by the EWSR1 gene located at band 12.2 of the long arm of chromosome 22; 2) the FUS protein encoded by the FUS gene located at band 16 on the short arm of chromosome 16; and 3) the TAF15 protein encoded by the TAF15 gene located at band 12 on the long arm of chromosome 7 The FET in this protein family's name derives form the first letters of FUS, EWSR1, and TAF15.
Ischemic fasciities (IF), also termed atypical decubital fibroplasia or decubital ischemic fasciitis, is a rare pseudosarcomatous tumor. It was first described by E. A. Montgomery et al. in 1992. This tumor typically forms in the subcutaneous tissues that overlie bony protuberances such as a hip in individuals who are debilitated and bed-ridden.
Cellular angiofibroma (CAF) is a rare, benign tumor of superficial soft tissues that was first described by M. R. Nucci et al. in 1997. These tumors occur predominantly in the distal parts of the female and male reproductive systems, i.e. in the vulva-vaginal and inguinal-scrotal areas, respectively, or, less commonly, in various other superficial soft tissue areas throughout the body. CAF tumors develop exclusively in adults who typically are more than 30 years old.
Angiofibroma of soft tissue (AFST), also termed angiofibroma, not otherwise specified, is a recently recognized and rare disorder that was classified in the category of benign fibroblastic and myofibroblastic tumors by the World Health Organization in 2020. An AFST tumor is a neoplasm that was first described by A. Mariño-Enríquez and C.D. Fletcher in 2012.
Low-grade myofibroblastic sarcoma (LGMS) is a subtype of the malignant sarcomas. As it is currently recognized, LGMS was first described as a rare, atypical myofibroblastic tumor by Mentzel et al. in 1998. Myofibroblastic sarcomas had been divided into low-grade myofibroblastic sarcomas, intermediate‐grade myofibroblasic sarcomas, i.e. IGMS, and high‐grade myofibroblasic sarcomas, i.e. HGMS based on their microscopic morphological, immunophenotypic, and malignancy features. LGMS and IGMS are now classified together by the World Health Organization (WHO), 2020, in the category of intermediate fibroblastic and myofibroblastic tumors. WHO, 2020, classifies HGMS as a soft tissue tumor in the category of tumors of uncertain differentiation. This article follows the WHO classification: here, LGMS includes IGMS but not HGMS which is a more aggressive and metastasizing tumor than LGMS and consists of cells of uncertain origin.